Anaemia is present when there is a decrease in the level of Hb in the blood below the reference level for the age and sex of the individual (Table 6.1). Alterations in the level of Hb may occur as a result of changes in the plasma volume, as shown in Fig. 6.6. A reduction in the plasma volume will lead to a spuriously high Hb-this is seen with dehydration and in the clinical condition of stress polycythaemia. A high plasma volume, such as in pregnancy, may produce a spurious anaemia. After a major bleed, anaemia may not be apparent for several days until the plasma volume returns to normal.
Patients with anaemia may be asymptomatic. A very slowly falling level of Hb allows for haemodynamic compensation and enhancement of the oxygen-carrying capacity of the blood. A rise in 2,3-DPG causes a shift of the oxygen dissociation curve to the right, so that oxygen is more readily given up to the tissues. Where blood loss is more rapid or severe, particularly in elderly people, symptoms may occur.
• Systolic flow murmur
• Cardiac failure
• Rarely papilloedema and retinal haemorrhages after an acute bleed (can be accompanied by blindness) Specific signs of the different types of anaemia will be discussed in the appropriate section. Examples include:
• Koilonychia-spoon-shaped nails seen in iron deficiency anaemia
• Jaundice-found in haemolytic anaemia
• Bone deformities-found in thalassaemia major
• Leg ulcers-occur in association with sickle cell disease
It must be emphasized that anaemia is not a diagnosis, and a cause must be found.
The various types of anaemia, classified in terms of the -Fed cell indices, particularly the Mev, are shown. There are three major types of anaemia:
• Hypochromic microcytic with a low Mev
• Normochromic normocytic with a normal Mev
• Macrocytic with a high Mev
A low Hb should always be considered in relation to:
• The white cell count
• The platelet count
• The reticulocyte count (as this indicates marrow activity)
• The blood film, as abnormal red cell morphology may indicate the diagnosis
Where two populations of red cells are seen, the blood film is said to be dimorphic. This may, for example, be seen in patients with ‘double deficiencies’, i.e. combined iron and folate deficiency in coeliac disease, or following treatment of anaemic patients with the appropriate haematinic.
Examination of the bone marrow is performed to investigate abnormalities found in the peripheral blood (Practical box 6.1). Aspiration provides a film which can be examined by microscopy for the morphology of the developing haemopoietic cells. The trephine provides a core of bone which is processed as a histological specimen and allows an overall view of the bone marrow architecture, cellularity and presence/absence of abnormal infiltrates. The following are assessed:
• Cellularity of the marrow
• Type of erythropoiesis, e.g. normoblastic or megaloblastic
• Cellularity of the various cell lines
• Infiltration of the marrow
• Assessment of iron stores
• Special tests may be performed: cytogenetic, immunological, cytochemical markers, biochemical analyses (e.g. deoxyuridine suppression test), microbiological culture.